<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .sky::-webkit-input-placeholder {
            color: red;
        }
    </style>
</head>

<body>
    <input type="text" class="sky" placeholder="sky测试用">
</body>
<script>
</script>

</html>